1. Technical Field
The present invention relates to a technique for performing gray-scale display control by a subfield driving method.
2. Related Art
As a method for expressing gray scales in an electro-optic device using electro-optic elements such as liquid crystal, so-called subfield driving has been known. In the subfield driving, one frame is divided into a plurality of subfields. The subfield driving is a method for performing gray-scale expression using a combination of ON and OFF of the plurality of subfields as a temporal integral value. The number of gray scales capable of being expressed in the subfield driving is determined in principle by the number of subfields. That is, for increasing the number of gray scales, it is necessary to increase the number of subfields per frame. In contrast to this, JP-A-2007-148417 discloses a technique for increasing the number of gray scales capable of being expressed by utilizing the transient response characteristics of liquid crystal without increasing the number of subfields per frame.
In recent years, systems which allow a user to view a three-dimensional (3D) video are under development. One example of methods for allowing a user to view a 3D video is a frame sequential method. The frame sequential method is a method which alternately displays time-divisionally a left-eye image and a right-eye image in a display device to allow a user to view the video via glasses whose shutters for the left eye and the right eye are opened and closed in synchronization with the video. In the case of a two-dimensional (2D) video, all subfields of one frame can be used to perform gray-scale expression. In the case of a 3D video, however, only one-half as many as the subfields of a 2D video can be used at most because a left-eye image and a right-eye image are displayed in one frame. Further in the frame sequential method, since a period during which both of the shutters for the left eye and the right eye are closed is disposed for reducing crosstalk between a left-eye image and a right-eye image, also subfields of this period cannot be used for gray-scale expression. The problem that the number of subfields capable of being used for gray-scale expression is limited occurs not only in a 3D video system, but also in a system or the like in which illumination is turned off in a pulse fashion in synchronization with the video for improving the quality of a moving image. This problem is common to systems in which a video is viewed via a blocking unit which blocks the field of view in a predetermined non-viewing period.